Integrated circuits are made in a bulk parallel process by patterning and processing semiconductor wafers. Each wafer contains many identical copies of the same integrated circuit referred to as a “die.” It may be preferable to test the semiconductor wafers before the die is cut into individual integrated circuits and packaged for sale. If defects are detected the defective die can be culled before wasting resources packaging a defective part. The individual die can also be tested after they have been cut into individual integrated circuits and packaged.
To test a wafer or an individual die—commonly called the device under test or DUT—a microelectromechanical (termed MEMS) probe card assembly is used which comes into contact with the surface of the DUT. The probe card generally contains three unique characteristics: (1) an XY array of individual probes that move in the Z direction to allow contact with the die pad; (2) an electrical interface to connect the card to a circuit test apparatus; and (3) a rigid reference plane defined in such a way that the probe card can be accurately mounted in the proper location. When the probe card is brought in contact with the die pad, the Z-direction movement allows for a solid contact with the probe tip. The probe card ultimately provides an electrical interface that allows a circuit test apparatus to be temporarily connected to the DUT. This method of die testing is extremely efficient because many die can be tested at the same time. To drive this efficiency even higher, probe card manufactures are making larger probe cards with an ever-increasing numbers of probes.
Currently two types of probe designs are used to test a semiconductor die—cantilever and torsional. FIGS. 7A and 7B illustrate a conventional cantilever probe. The probe (705) comprises a probe tip (710), a bending element (715), and a probe base (720), which is mounted to a substrate (725). This entire structure is referred to herein as the probe card. The entire probe card is generally moved in the Z-direction (depicted by arrow 730) causing the bending element (715) to bend, allowing the probe tip (710) to come into contact with the die pad that is under test. FIG. 7B illustrates how the probe bending element (735) bends while being brought into contact with the die. As an individual probe travels to make contact with the DUT contact pad (this event is called a touchdown), the probe tip scrubs the contact pad, which perfects an electrical contact with the die such that testing can commence. The die contact pads, which are typically aluminum, are often coated with a thin layer of aluminum oxide, or other protective coating, and the probe tip must cut through the coating to perfect the electrical connection. Once testing is complete, the probe (705) is moved away from the die pad and the probe springs back to its original position.
The second type of probe is based on a torsional design. For example, U.S. Pat. No. 6,426,638 describes a torsion spring design. FIG. 8 illustrates a torsional probe design. As the probe tip (81) comes in contact with the DUT contact pad, it moves flexibly in response to force applied vertically to the tip (81). Vertical movement of the tip (81) depresses the arm (82) and torsionally flexes the torsion element (83) in the direction indicated by arrow (90). The torsion element (83) serves as a torsional spring, thereby impressing a restoring force on the tip (81).
These probes, either the torsional or the cantilever, can become damaged and must be replaced. The damage may be from repetitive use. For example, an individual probe may experience thousands of touchdowns and become damaged through ordinary wear and tear. Another possibility is that the probe is defective from the beginning and it breaks prematurely. And yet another possibility is that the probe card is mishandled and the probes are damaged. Regardless of the reason for the damage, it is often advantageous to repair the damaged probe and bring the entire probe card back into service.
To repair a probe card using conventional techniques, the manufacturer of the probe card must first create a new probe, remove the damaged probe from the probe card and install the new probe on the probe card. For example, U.S. Pat. Nos. 5,190,637, 6,436,802, 6,452,407, 6,297,164 and 6,520,778 describe methods for constructing probe structures. U.S. Pat. No. 6,777,319 describes a method of repairing at spring contact by first removing the spring contact by either cutting the spring contact and leaving a stub, or by localized heating that causes the solder to release the spring. U.S. Pat. No. 6,523,255 also describes a method of repairing a damaged probe wire where the damaged probe wire is removed by “pulling on the wire until it fractures at the base of the wire.”
These techniques however, have several drawbacks. For example, it may take several weeks to build a new probe. Not only does this cause tremendous inefficiencies by pulling the probe card off the assembly line, but construction of a few replacement probes after the fact can be very expensive. Also, the newly constructed probes will likely not have the same characteristics of the original probes because of variations in manufacturing techniques. This means that the newly replaced probe will likely perform differently than the other probes on the probe card, resulting in potential inefficiencies when the repaired probe card is placed back into service. In addition, the current techniques for removing the damaged probe as described in U.S. Pat. Nos. 6,523,255 and 6,777,319 can be clumsy and can damage other probes in the immediate area.
What is needed, therefore, is a structure and method for repairing MEMS probe cards that is inexpensive, fast and accurate.